Stabilize @file command line arguments

Issue rust-lang#63576

Author: jsgf

src/librustc_driver/args.rs

@@ -3,22 +3,12 @@ use std::fmt;
 use std::fs;
 use std::io;
 use std::str;
-use std::sync::atomic::{AtomicBool, Ordering};
-
-static USED_ARGSFILE_FEATURE: AtomicBool = AtomicBool::new(false);
-
-pub fn used_unstable_argsfile() -> bool {
-    USED_ARGSFILE_FEATURE.load(Ordering::Relaxed)
-}
 
 pub fn arg_expand(arg: String) -> Result<Vec<String>, Error> {
     if arg.starts_with("@") {
         let path = &arg[1..];
         let file = match fs::read_to_string(path) {
-            Ok(file) => {
-                USED_ARGSFILE_FEATURE.store(true, Ordering::Relaxed);
-                file
-            }
+            Ok(file) => file,
             Err(ref err) if err.kind() == io::ErrorKind::InvalidData => {
                 return Err(Error::Utf8Error(Some(path.to_string())));
             }

src/librustc_driver/lib.rs

@@ -1043,12 +1043,6 @@ pub fn handle_options(args: &[String]) -> Option<getopts::Matches> {
     //   (unstable option being used on stable)
     nightly_options::check_nightly_options(&matches, &config::rustc_optgroups());
 
-    // Late check to see if @file was used without unstable options enabled
-    if crate::args::used_unstable_argsfile() && !nightly_options::is_unstable_enabled(&matches) {
-        early_error(ErrorOutputType::default(),
-            "@path is unstable - use -Z unstable-options to enable its use");
-    }
-
     if matches.opt_present("h") || matches.opt_present("help") {
         // Only show unstable options in --help if we accept unstable options.
         usage(matches.opt_present("verbose"), nightly_options::is_unstable_enabled(&matches));